I wanna replace my psu due to a new pc build the one I have is very large if I was gonna compare it to summit its half the size of a netbooks keyboard (hinges to trackpad) and its only pumping out 30watts.
My question is 1. can i get a smaller size psu
2. the cables that attach to the mother board I asume I have to buy them seprate....ones I have are solderd into the psu

My question is 1. can i get a smaller size psu 2. the cables that attach to the mother board I asume I have to buy them seprate....ones I have are solderd into the psu

PSUs tend to be pretty standard sizes, aimed at particular case sizes and in most of them the cables are integral. I have read of PSUs with plug in cables, but I don't recall what brand they were.
In the past I was happy to recommend Antec PSUs, but I've had two fail in recent years. Thus far, a more recent purchase of a Corsair PSU seems to be going well (two and a half years old now).

see the reason Im asking is my pc case is falling apart and my 3.5 hardrive is fooked plus my psu is faulty as hell

so I thought about asking my friend (he makes body kits for cars) to make me a new case something small but obv to take my motherboard and to have bays for 2.5 drives

Iv looked on the market for a new case and they all seem to be standard size I really dont have the space in my small flat to store a standard size pc and sine my mother board is fine may as well put it to use plus my friend owes me a few favours

I'm sure he does, but given your question I'm fairly confident neither of you have any idea what you're doing... Not only does the resin-based enclosure make a serious fire-hazard, but I doubt either of you have given any consideration to airflow inside the box, cooling in general and accessibility. Note that the extreme case-modders like those on the mini-itx website use low-spec and low-power systems to keep the heat build-up in check, or design a case that provides sufficient cooling capacity to keep things safe...